Scientific Forecaster Discussion

Area forecast discussion for western South Dakota and northeastern Wyoming National Weather Service Rapid City South Dakota 1034 am MST Tuesday Mar 3 2015

Update... issued at 1028 am MST Tuesday Mar 3 2015

Conditions continue to improve on most of the South Dakota plains...far northeast Wyoming...northern Black Hills. Latest guidance continue to show secondary shortwave dropping to our west which will support -sn over parts of northeast Wyoming through this afternoon. Downstream convergence signature noted on radar and model guidance for far southwest South Dakota. Headlines adjusted to account.

Update issued at 753 am MST Tuesday Mar 3 2015

Looking at latest web cams...radar loops...and 12z rap...will shave some of the northern part of the Winter Weather Advisory. Good drying coming in and less snow than expected across northwest South Dakota...so even with gusty winds...blowing snow should be limited.

Merging upper level troughs and associated reflected fgen response continuing to traverse the region this morning. A decent band of moderate snow is in place as of 09z across western South Dakota...where fgen/uvm/lsa are currently coupled and maximized with this system. This band will quickly shift NE early this morning...with general light snow continuing in is wake through most of the morning. Sig bl drying will occur this afternoon as Arctic high pressure builds into the region. Save for a weak upslope response tonight in the Northern Hills...dry weather expect to prevail most places tonight through Wednesday.

Today...primary shortwave and associated lobe of ascent will shift quickly NE of the forecast area. This will support a quick wane to snow...with generally 1-3 additional inches expected where advisories/warnings are currently in place. Biggest impact will be gusty northwest winds on the South Dakota plains. Sustained winds of 15 to 25 miles per hour with gusts over 40 will continue through morning. However...latest model guidance favors a quicker wane to wind speeds this afternoon than previous forecast model suites suggested. In addition...upslope snows will quickly wane as bl drying highly impacts snow production there by late morning. Hence...many of the headlines could likely be dropped late this morning...on track with most headline expirations. Will drop the far northwest South Dakota zones from the winter weather advection. Snow has not really materialized there and at most only a couple tenths expected in areas that do see snow. The only location that looks to see snow accums into the afternoon is the southern Black Hills where eddy convergence is expected...although only a couple additional inches at most would be expected there into the afternoon. Otherwise...cold conds on track with temperatures falling through the day.

Tonight...dry conds expected most locations. Main northern steam trough axis will traverse the region tonight...possibly supporting a weak upslope response in the Northern Hills. Bl moisture is pretty limited...hence snow probs remain very low. Isallobaric wind will prevail tonight across the region...supporting sustained northwest winds. This will support near windchill advection conds across the northwest South Dakota zones.

Wednesday...surface ridge will build into the region with dry weather and clear skies expected. Cold conds will prevail with most locations struggling out of the teens. Warm air advection will ensue Wednesday night...with typical downslope locations seeing rising temperatures after midnight.

Arctic high slides well east...as upper flow becomes more westerly. Warmer air will begin to build into the region on Thursday. Medium range models generally in good agreement for the rest of the week and the weekend as mainly dry northwest flow aloft remains through the period. A ridge over the western Continental U.S. Will slowly move east into The Rockies over the weekend. Temperatures will be above average Friday through Monday...with highs in the 40s and 50s.

Snow has tapered off and ended in most areas this morning...except for across far southwest South Dakota and portions of northeast Wyoming. Snow will end across northeast Wyoming early this afternoon...including at kgcc...while areas of snow will linger across the southern Black Hills and far southwest South Dakota through the afternoon. Areas of MVFR conditions will persist across northeast Wyoming into southern South Dakota through the afternoon...with local IFR conditions over far southwest South Dakota. Gusty northwest winds to 35 kts will persist into the early afternoon across the South Dakota plains...then gradually diminish late this afternoon and early evening. VFR conditions are generally expected tonight.